How the building blocks of life reached the early Earth

Recent research brings us one step closer to understanding how Earth got the building blocks that were responsible for sparking life on the planet, and how were are all here now reading this article.

The crux of the matter? Scientists recently discovered that zinc contained in meteorites and other ‘unmelted’ asteroids, also known as planetesimals, holds the key to solving this puzzle.

Volatiles like zinc hitched a ride

Volatiles are substances that easily turn into gases at relatively low temperatures. Think of things like water, carbon dioxide, methane, and ammonia.

In planetary science, we often refer to volatiles as elements or compounds with low boiling points that are key to the makeup of atmospheres and oceans.

When planets form, they tend to trap these volatiles in their rocks or ice. Over time, heat and geological activity can release them, causing events like volcanic eruptions or even helping to form atmospheres.

Studying volatiles is super important for understanding planetary systems, including our own Earth. These substances can affect everything from climate to surface chemistry and are crucial for the potential of life.

That’s why scientists search for volatiles when looking for signs of life on other planets — they’re usually tied to biological processes.

Life’s building blocks and zinc

Pinning down the origin of these volatile elements on Earth is no small feat. Still, our scientists aren’t afraid of a good mystery.

They’ve found that a particular composition of zinc, unique to meteorites, can help identify the sources of Earth’s volatiles.

Going into the complexities of our Solar System, scientists discovered that Earth’s zinc has an intriguing origin story of its own.

“One of the most fundamental questions on the origin of life is where the materials we need for life to evolve came from,” said Dr Rayssa Martins from Cambridge’s Department of Earth Sciences.

“If we can understand how these materials came to be on Earth, it might give us clues to how life originated here, and how it might emerge elsewhere.”

As it turns out, the answers to life’s origins may lie in zinc and the tiny bodies that make up our rocky planets.

Role of Planetesimals

Planetesimals, the compact bodies formed through a process known as accretion, are the unsung heroes in the formation of rocky planets like ours.

However, they are not all created equal. Early planetesimals exposed to high levels of radioactivity melted, losing their precious volatiles.

But some planetesimals, the late bloomers that formed after the peak of radioactivity, survived the melting process, thereby preserving their volatile elements.

In a study published in Science Advances, Dr. Martins and her colleagues delved into the varying forms of zinc that arrived on Earth from these planetesimals.

Their research involved measuring the zinc content of a vast sample of meteorites from different planetesimals and tracing the path of Earth’s accretion, a journey spreading over tens of millions of years.

Zinc’s tale of life’s origins

Their findings are nothing short of fascinating. The melted planetesimals, despite contributing about 70% to Earth’s overall mass, seemed to have provided only around 10% of its zinc.

Where did the rest come from? It appears that materials that did not melt and lose their volatile elements were rich in zinc. These unmelted, or ‘primitive’ materials, as they are called, were vital sources of volatiles for Earth.

“We know that the distance between a planet and its star is a determining a factor in establishing the necessary conditions for that planet to sustain liquid water on its surface,” said Martins, the study’s lead author.

“But our results show that there’s no guarantee that planets incorporate the right materials to have enough water and other volatiles in the first place – regardless of their physical state.”

Study implications

The implications of this research are far-reaching. Understanding the movement of elements like zinc through millions or even billions of years could be a critical instrument in the search for life elsewhere, such as on Mars or planets outside our Solar System.

“The roles these different materials play in supplying volatiles is something we should keep in mind when looking for habitable planets elsewhere,” Martins emphasized.

This research pushes us closer to understanding the complex interplay of elements that kick-started life on Earth. And, eventually, it might even lead us to discovering life in the vast expanse of the cosmos.

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This important study was supported in part by both Imperial College London and the European Research Council (ERC), along with UK Research and Innovation (UKRI),

The study is published in the journal Science Advances.

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